Metal-coated polyimide film

ABSTRACT

A metal-coated polyimide film is excellent in long-term adhesion reliability, exhibits various dimensional stabilities, and is particularly suitable for FPC, COF and TAB applications. The metal-coated polyimide film comprises a non-thermoplastic polyimide film; and a metal layer being directly formed on one surface or both surfaces of the non-thermoplastic polyimide film without using an adhesive, wherein the non-thermoplastic polyimide film contains a non-thermoplastic polyimide resin having a thermoplastic polyimide block component.

PRIORITY

This application is a continuation of U.S. patent application Ser. No.12/012,275, filed Feb. 1, 2008, now U.S. Pat. No. 8,158,268 which is acontinuation in part of International Application No. PCT/JP2006/315403,with an international filing date of Aug. 3, 2006, now abandoned, whichin turn claims priority to Japanese Patent Application No. 2005-226241,filed Aug. 4, 2005. All of the above applications are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a metal-coated polyimide filmpreferably used for electronic materials such as a flexible printedcircuit (“FPC”), a flexible printed board, a flexible printed wiringboard, a base film for Chip on Film (“COF”), and a tape-automatedbonding (“TAB”) tape.

BACKGROUND ART

Conventionally, polyimide resin having various superior properties, suchas heat resistance and electrical isolation performance, has been widelyused in the field of electronics. For example, films made from polyimideresin have been used for a flexible printed board, a TAB tape, and abase film for high-density storage medium. Polyimide resin has been usednot only in the form of a film but also in various forms including asheet and a coating agent. In a case where polyimide resin is used inthe form of a film, the film is not always used alone. The film has beenwidely used in a laminated structure, like a structure in which a copperfoil is bonded to the surface of the film with an adhesive, a structurein which the surface of the film is subjected to copper sputtering orcopper electroplating, and a structure in which polyimide resin is castor coated on a copper foil.

With the recent advance of technology of electronic materials anddevices, a polyimide film used has been required to have more complexand much more properties other than basic properties such as heatresistance, isolation performance, and solvent resistance. For example,with the downsizing of electrical and electronic devices, flexibleprinted boards used in the devices are required to have fine wiringpatterns. This requires polyimide films that exhibit smaller changes indimension caused by heating and tension. The lower the linear expansioncoefficient is, the smaller the amount of change in dimension caused byheating is. Moreover, the higher the elasticity modulus is, the smallerthe amount of change in dimension caused by tension is. However, thepolyimide films with high elasticity modulus and low linear expansioncoefficient are generally produced using rigid monomers with highlinearity, including pyromellitic dianhydride and p-phenylene diamine,for example. This gives rise to the following at least two problems: Oneproblem is that the resulting films are inferior in flexibility and alsoinferior in bending properties which are required for flexible printedboards. The second problem is that inappropriate use of the monomersproduces films having high water absorbency and high moisture expansioncoefficient.

For example, in a case where the polyimide film is used for asemiconductor package, the polyimide film is required to havedimensional stability against heat and tension and dimensional stabilityunder the conditions where moisture is absorbed. Therefore, a polyimidefilm having low linear expansion coefficient, high elasticity modulus,and low moisture expansion coefficient is desirable.

Furthermore, a finer wiring pattern has been formed on a polyimide filmfor use in a flexible printed board. As a result of this, the demand formetal-laminated polyimide film in which a thin-film metal that allowsfor the formation of a fine pattern is laminated has been increasing.This demand cannot be met by the method conventionally used in mostcases. That is, the method in which a thin copper foil is laminated onthe surface of polyimide film with the use of an adhesive such as athermoplastic polyimide adhesive or epoxy adhesive makes it difficult tolaminate a thin copper film suitable for a fine pattern thereon.

In view of this, as a method for producing a metal-laminated boardwithout using an adhesive, a method of directly forming a metal withoutusing an adhesive has been adopted in most cases, like a method in whicha thin metal film is formed on the surface of polyimide film by using asputtering apparatus or a metal vapor deposition apparatus, and thencopper is laminated on the metal film by plating. The adoption of thismethod makes it possible to change a thickness of the metal layer to athickness in the range from not less than 1 μm to several tens ofmicrometers as appropriate. In particular, since this technique allowsfor the formation of a thin film, it also has the feature that a metallayer having a thickness suitable for a fine pattern can be formed.

However, the above method has the following problem: Adherabilitybetween the film and the metal layer in the laminated board is lowerthan adherability obtained by a method using an adhesive, and theadherability obtained by the above method tends to decrease especiallywhen an environmental resistance test is conducted. On this account, theimprovement to a polyimide film has been required.

Patent Documents 1 and 2 disclose a polyimide film which is produced byusing p-phenylenebis(trimellitic acid monoester anhydride) with the aimof decreasing water absorbency and moisture expansion coefficient.However, the polyimide film disclosed in Patent Documents 1 and 2 isinstable in an environmental test, and reliability of the polyimide filmdecreases when the polyimide film is used for COF or the like.

Further, in the case of a method in which a metal layer is directlyformed by sputtering, vapor deposition, or the like without using anadhesive, it is different in its production process from a method inwhich a metal foil is laminated with the use of an adhesive. Forexample, metal sputtering requires that a state within the system ischanged to a nearly vacuum state in the process of sputtering. However,it is desired that a state within the system should be changed to avacuum state as soon as possible in consideration of productivity.

Patent Document 3 discloses a polyimide film which is produced by usingthe following five components: p-phenylenebis(trimellitic acid monoesteranhydride); pyromellitic dianhydride; biphenyltetracarboxylicdianhydride; p-phenylene diamine; and diaminodiphenylether. PatentDocument 3 also discloses that adherability increases in a case where ametal layer is directly formed on the polyimide film by vapordeposition, sputtering, or the like without using an adhesive. However,the technical feature of Patent Document 3 is that types andcompositions of monomers to be used are selected, and therefore totallydifferent from that of the present invention.

Meanwhile, there is a known method in which polymerization is carriedout at multiple stages to produce polyimide resin having a blockcomponent. For example, Patent Documents 4 and 5 disclose the followingmethod as a method of polymerizing a block component in advance: apolyamic acid consisting of phenylenediamine and pyromelliticdianhydride or a polyamic acid consisting of phenylenediamine and 3,3′-,4,4′-benzophenonetetracarboxylic acid is polymerized to form a blockcomponent of the polyamic acid, and imide is added to the obtained blockcomponent, whereby a copolymerized polyimide having a block component isproduced. However, neither Patent Document 4 nor Patent Document 5includes a step of forming a thermoplastic block component.

Thus, the technical idea has never been known of designing a film sothat a thermoplastic polyimide block component is present in the film byusing non-thermoplastic polyimide resin containing a thermoplasticpolyimide block component, and the film is non-thermoplastic as a whole.

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 11-54862

Patent Document 2: Japanese Unexamined Patent Application PublicationNo. 2001-72781

Patent Document 3: Japanese Unexamined Patent Application PublicationNo. 2004-137486¥

Patent Document 4: Japanese Unexamined Patent Application PublicationNo. 2000-80178

Patent Document 5: Japanese Unexamined Patent Application PublicationNo. 2000-119521

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

The present invention has been attained to solve the above problems, andan object thereof is to provide a metal-coated polyimide film which isobtained by directly forming a metal layer on a polyimide film withoutthe use of an adhesive, and which is excellent in adherability andvarious dimensional stabilities (dimensional stability against heat andtension and dimensional stability under the conditions where moisture isabsorbed).

Means for Solving the Problems

To achieve this object, the present inventors have conducted extensivestudies and found that a polyimide film containing a polyimide whosemolecules are adequately designed exhibits high adherability even when ametal layer is directly formed on the polyimide film without using anadhesive. The present invention has been made based on this finding. Inparticular, the present invention can solve the above-described problemby providing a novel metal-coated polyimide film in accordance with anyof the embodiments described below:

1) A metal-coated polyimide film comprising: a non-thermoplasticpolyimide film; and a metal layer being directly formed on one surfaceor both surfaces of the non-thermoplastic polyimide film without usingan adhesive, wherein the non-thermoplastic polyimide film contains anon-thermoplastic polyimide resin having a thermoplastic polyimide blockcomponent.

2) The metal-coated polyimide film described in 1), wherein thethermoplastic block component is present in an amount of 20 to 60 mol %of the entire non-thermoplastic polyimide resin.

3) The metal-coated polyimide film described in 1) or 2), wherein thediamine component in the thermoplastic polyimide block componentcontains 2,2-bis(4-aminophenoxyphenyl)propane.

4) The metal-coated polyimide film described in any of 1) through 3),wherein the acid component in the thermoplastic polyimide blockcomponent contains a benzophenonetetracarboxylic acid and/or abiphenyltetracarboxylic acid.

5) The metal-coated polyimide film described in any of 1) through 4),wherein the number n of repeating units of the thermoplastic polyimideblock component is 3 to 99.

6) The metal-coated polyimide film described in 5), wherein the number nof repeating units of the thermoplastic polyimide block component is 4to 90.

7) The metal-coated polyimide film described in any of 1) through 6),wherein the non-thermoplastic polyimide film is a polyimide filmconsisting of a non-thermoplastic polyimide resin having a thermoplasticpolyimide block component.

8) The metal-coated polyimide film described in any of 1) through 6),wherein the non-thermoplastic polyimide film further contains a fillerand a non-thermoplastic polyimide resin having a thermoplastic polyimideblock component.

9) The metal-coated polyimide film described in 8), wherein thenon-thermoplastic polyimide resin having the thermoplastic polyimideblock component is 50 wt % or more of the polyimide film.

10) The metal-coated polyimide film described in 1), wherein the metallayer has a metal layer A formed by dry film forming method.

11) The metal-coated polyimide film described in 10), wherein the metallayer A has: a metal layer A1 that contacts the non-thermoplasticpolyimide film; and a metal layer A2 formed on the metal layer A1.

12) The metal-coated polyimide film described in 10) or 11), wherein thedry film forming method is any method selected from sputtering, ionplating, and vapor deposition.

13) The metal-coated polyimide film described in 11), wherein the metallayer A1 contains at least one metal selected from the group consistingof Ni, Cu, Mo, Ta, Ti, V, Cr, Fe, and Co.

14) The metal-coated polyimide film described in any of 10) through 13),wherein a metal layer is formed on the metal layer A by electrolessplating or electroplating.

15) The metal-coated polyimide film described in any of 10) through 13),further comprising: (i) a metal layer being formed on the metal layer Aby electroless plating; and (ii) a metal layer being formed on the metallayer (i) by electroplating.

16) A metal-coated polyimide film comprising: a base metal layer beingformed on one surface or both surfaces of a non-thermoplastic polyimidefilm containing non-thermoplastic polyimide resin having thermoplasticpolyimide block component by dry film forming method; and a conductivelayer being formed on the metal layer by at least one of sputtering,electroplating, and electroless plating.

16) A flexible printed wiring board including a metal-coated polyimidefilm according to any of 10 through 16.

17) A base polyimide film used in a method for producing a metal-coatedpolyimide film in which a metal layer is directly formed on a polyimidefilm without using an adhesive while vacuum suction is carried out witha vacuum pump, wherein the polyimide film contains a non-thermoplasticpolyimide resin having a thermoplastic polyimide block component.

Additionally, a method is provided for preparing a metal-coatedpolyimide film comprising:

a) providing a non-thermoplastic polyimide film containing anon-thermoplastic polyimide resin having a thermoplastic polyimide blockcomponent;

b) applying vacuum suction to the polyimide film; and

c) forming a metal layer directly on the polyimide film by a dry filmforming method without using an adhesive.

An additional method of preparing a metal-coated polyimide film isprovided, comprising:

a) providing a non-thermoplastic polyimide film having the valuerepresented by following equation (3):a water vapor transmission rate×thickness  (3)of at least about 2500 μm·g/m²/24 h;

b) applying vacuum suction to the polyimide film; and

c) forming a metal layer directly on the polyimide film by a dry filmforming method without using an adhesive.

In a preferred embodiment, the above method is carried out wherein thenon-thermoplastic polyimide film has a value represented by followingequation (3) of at least about 3000 μm·g/m²/24 h.

In certain method embodiments of the present invention, the dry filmforming method is any method selected from sputtering, ion plating, andvapor deposition.

Effects of the Invention

According to the present invention, it is possible to provide ametal-coated polyimide film which is excellent in long-term adhesionreliability and various dimensional stabilities and suitable for wiringboards for high-density package, such as COF.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing the relationship between water vaportransmission rate and thickness of material of sample of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The following will describe an embodiment of the present invention. Ametal-coated polyimide film of the present invention is obtained bydirectly forming a metal layer, without using an adhesive, on anon-thermoplastic polyimide film that contains a non-thermoplasticpolyimide resin having a thermoplastic polyimide block component.

The present inventors have studied various molecular designs forpolyimide. A polyimide film of the present invention is anon-thermoplastic polyimide film, but contains a thermoplastic polyimideblock component therein. More specifically, a polyimide film is obtainedby designing a polyimide resin that constitutes the film so as to be apolyimide resin whose molecule contains a thermoplastic polyimide blockcomponent and which is non-thermoplastic as a whole. The presentinventors have found that such a molecular design for the polyimideresin that constitutes a polyimide film gives some remarkable propertiesto a metal-coated film obtained by directly forming a metal layer on thepolyimide film without using an adhesive.

That is, a metal-coated polyimide film of the present invention is suchthat a non-thermoplastic polyimide film as a base material has lowlinear expansion coefficient, low moisture expansion coefficient, and amoderate elasticity modulus, and the non-thermoplastic polyimide filmhas excellent dimensional stabilities against various external changesthat are given to the metal-coated film. As a result of study made bythe present inventors, it was found that the above-designednon-thermoplastic polyimide film has a high water vapor transmissionrate. This means that the film humidifies and dehumidifies quickly.Therefore, it is possible to considerably enhance the productivity of ametal-coated polyimide film which is obtained by directly forming ametal layer by using a method that takes advantage of the aboveproperties, for example, by sputtering onto the polyimide film whilevacuum suction is carried out.

(Non-Thermoplastic Polyimide Film Used in the Present Invention)

The polyimide film of the present invention is produced by usingpolyamic acid as a precursor. The polyamic acid may be produced by anyknown method. Typically, substantially equimolar amounts of an aromaticacid dianhydride and aromatic diamine are dissolved in an organicsolvent to prepare a polyamic acid organic solvent solution, and thissolution is stirred under controlled temperature conditions untilpolymerization of the acid dianhydride and the diamine is completed. Thepolyamic acid solution is usually obtained at a concentration of 5 to 35wt % and preferably 10 to 30 wt %. A solution having a concentrationwithin this range has an adequate molecular weight and an adequatesolution viscosity.

Various known processes and combinations of these processes may beemployed as the polymerization process. The key feature of thepolymerization process for producing polyamic acid is the order ofadding the monomers. The physical properties of the resulting polyimideare adjusted by controlling the order of adding the monomers. Thus, inthe present invention, any process of adding monomers may be employedfor producing the polyamic acid. Representative examples of thepolymerization processes are as follows:

1) A process including dissolving an aromatic diamine in an organicpolar solvent and reacting the aromatic diamine with a substantiallyequimolar amount of an aromatic tetracarboxylic dianhydride to conductpolymerization;

2) A process including reacting an aromatic tetracarboxylic dianhydrideand fewer moles of an aromatic diamine in an organic polar solvent toprepare a prepolymer having acid anhydride groups at the both ends andpolymerizing at multiple stages the prepolymer with an aromatic diamineso that the aromatic tetracarboxylic dianhydride and the aromaticdiamine both used in the entire process of polymerization aresubstantially equimolar;3) A process including reacting an aromatic tetracarboxylic dianhydrideand excess moles of an aromatic diamine in an organic polar solvent toprepare a prepolymer having amino groups at the both ends, adding anadditional aromatic diamine to the prepolymer, and then polymerizing atmultiple stages the resulting mixture with an aromatic tetracarboxylicdianhydride so that the aromatic tetracarboxylic dianhydride and thearomatic diamine both used in the entire process of polymerization aresubstantially equimolar;4) A process including dissolving and/or dispersing an aromatictetracarboxylic dianhydride in an organic polar solvent and polymerizingthe aromatic tetracarboxylic dianhydride with a substantially equimolaramount of an aromatic diamine; and5) A process including reacting a substantially equimolar mixture of anaromatic tetracarboxylic dianhydride and an aromatic diamine in anorganic polar solvent to conduct polymerization.

Any one or combination of these processes may be employed.

The polyimide resin that constitutes the non-thermoplastic polyimidefilm of the present invention contains a thermoplastic polyimide blockcomponent in the molecule, but is designed so that the film functions asa non-thermoplastic polyimide film as a whole. Such a design concept ofthe polyimide film that is a base material of the metal-coated polyimidefilm is important in the present invention. The polyimide resin having athermoplastic block component makes it possible to solve variousproblems associated with a metal-coated film wherein a metal layer isdirectly formed without using an adhesive. A preferable polymerizationprocess for obtaining such a polyimide resin is a process includingpreparing a block component of the thermoplastic polyimide precursor(polyamic acid prepolymer that imparts thermoplastic polyimide) andsubsequently preparing a precursor of the non-thermoplastic polyimideusing the remaining diamine and/or acid dianhydride. This process isideal for preparing the thermoplastic block component. Here, it ispreferable to adopt any partial combination of two or more of theprocesses 1) to 5). Particularly, the processes 2) and 3) are preferablein that they ensure introduction of a thermoplastic polyimide blockcomponent.

For example, in the process 2) or 3) above, the prepolymer may be madeby controlling the composition so that a thermoplastic polyimide isyielded by reacting equimolar amounts of the aromatic tetracarboxylicdianhydride and the aromatic diamine compound, and adequate aromatictetracarboxylic dianhydride and aromatic diamine compound used in theentire process may be selected so that the final product, polyimide,exhibits non-thermoplastic properties.

For example, a polyamic acid solution may be obtained as follows: Afterdissolving 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) in DMF, i.e.,N,N-dimethylformamide, pyromellitic dianhydride (PMDA) and3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) are added sothat the total amount of anhydride is smaller relative to BAPP toprepare a thermoplastic polyimide block component (polyamic acidprepolymer that imparts thermoplastic polyimide). After that,p-phenylene diamine (p-PDA) is dissolved in the resulting prepolymersolution, and PMDA is added to the prepolymer solution so that the totalof the acid dianhydride used in the entire process is substantiallyequimolar to the amount of diamine. Thereby, a polyamic acid solution isobtained.

Here, the “thermoplastic polyimide block component” refers to acomponent that gives a film that softens and does not retain itsoriginal shape after 1 minute of heating at 450° C. on a fixing frame.There are two types of evaluation of a polyimide block componentdepending on its purpose. One evaluation is for judgment of whether thepolyimide block component is thermoplastic, and another is for furtherdetermination of how thermoplastic the polyimide block component is. Forpurposes of evaluation of whether a polyimide block component isthermoplastic, a block component film is prepared by reacting theamounts of dianhydride and diamine compounds that constitute the blockcomponent, and completing formation of the film by adding sufficientamount of additional dianhydride or additional diamine so that equimolaramounts of dianhydride and diamine are present in the composition,thereby forming a block component film (hereinafter, this film isreferred to as “the polyimide film composed of the thermoplasticpolyimide block component”).

The sample that is representative of the block component for evaluationpurposes can be prepared in two different ways. In a first evaluationsample preparation, the additional dianhydride or diamine used tocomplete the film formation of the block component is selected from thedianhydrides or diamines already used in the proposed thermoplasticpolyimide block component. This first sample preparation advantageouslyprovides an excellent model of the character of the block component.Where there is more than one dianhydride or diamine used in the proposedthermoplastic polyimide block component, the dianhydride or diamine usedto complete the film formation is that which contributes the highest Tgto the polyimide film composed of the thermoplastic polyimide blockcomponent. Alternatively, if there are two or more types of diaminecomponents that constitute the block component, the most rigid diaminecomponent can be selected as the additional diamine component. In asecond evaluation sample preparation, the additional dianhydride ordiamine used to complete the film formation is selected frompyromellitic acid dianhydride (in the case of the compound havingdiamine functionality) or p-phenylenediamine (in the case of thecompound having acid dianhydride functionality). This second samplepreparation has the advantage of providing a standard test for ease ofcomparison of different proposed thermoplastic polyimide blockcomponents. Unless otherwise indicated, this second sample preparationis intended for use in evaluation of all proposed thermoplasticpolyimide block components to determine if the block component isthermoplastic, and additionally for further determination of howthermoplastic the polyimide block component is.

For purposes of evaluation of how thermoplastic the polyimide blockcomponent is, the polyimide film composed of the thermoplastic polyimideblock component should be prepared at a low baking temperature by aknown method, for example, baking temperature of 300° C. and baking timeof 15 minutes. If a polyimide block component film for evaluation cannot be obtained due to melting at even such a low baking temperature,the block component used therein is deemed to have 300° C. or lessthermoplastic characteristics. If a polyimide block component film forevaluation can be obtained, the obtained film is then to be heated up tomelting. Thus the melting temperature of the film can be determined. Itis preferable that the melting temperature determined by such aprocedure is in a range of 250° C. to 450° C., preferably, in a range of300° C. to 400° C.

When the melting temperature of the polyimide block component film isexcessively low, it becomes difficult to produce an end productnon-thermoplastic polyimide film. When the melting temperature of thepolyimide block component film is excessively high, high adherability,which is the advantageous feature of the present invention, is rarelyobtainable.

In producing a prepolymer in the above processes 2) and 3), an aromatictetracarboxylic dianhydride component and an aromatic diamine componentare used in such a manner that either of them is higher in molarquantity. A molar ratio of the aromatic tetracarboxylic dianhydridecomponent to the aromatic diamine component, which is not particularlylimited, is preferably 100:85 to 100:95, or 100:105 to 100:115.

The technical feature of the present invention is that a thermoplasticblock component is ideally present in a non-thermoplastic polyimideresin. It is important that the block is thermoplastic as a whole, and arigid component can be used as monomers that constitute a thermoplasticblock component, as long as a thermoplastic block is formed with the useof such monomers.

The thermoplastic polyimide block component is preferably present in anamount of 20 to 60 mol %, more preferably 25 to 55 mol %, and mostpreferably 30 to 50 mol % of the entire polyimide.

When the content of the thermoplastic polyimide block component is belowthis range, high adherability may not be easily achieved, and when thecontent of the thermoplastic polyimide block component is above thisrange, it becomes difficult to obtain a non-thermoplastic polyimide filmas an end product.

For example, when the polymerization process described in 2) isemployed, the content of the thermoplastic polyimide block component isdetermined by the following equation (1):(Thermoplastic block component content)=a/Q×100  (1)wherein a is the amount (mol) of the acid dianhydride component used inproducing the thermoplastic polyimide block component, and Q is thetotal amount of the acid dianhydride component (mol).

When the polymerization process described in 3) is employed, the contentof the thermoplastic polyimide block component is determined by thefollowing equation (2):(Thermoplastic block component content)=b/P×100  (2)wherein b is the amount (mol) of the diamine component used in producingthe thermoplastic polyimide block component, and P is the total amount(mol) of the diamine.

The number n of the repeating units of the thermoplastic block componentis preferably 3 to 99 and more preferably 4 to 90. When n is below thisrange, high adherability is not easily obtained, and the moistureexpansion coefficient tends to increase. When n is beyond this range,the storage stability of the polyimide precursor solution tends todecrease, and the reproducibility of polymerization tends to decrease.

The thermoplastic polyimide block component in the present invention ispreferably one that gives a polyimide film having a glass transitiontemperature (Tg) in the range of 150° C. to 300° C. when the film ismade by the above-described process. The glass transition temperature Tgcan be determined based on the inflection point of the storage modulusdetermined with a dynamic viscoelasticity analyzer (DMA) or the like.

The monomers that form the thermoplastic polyimide block component ofthe present invention will now be described. A diamine componentpreferably used to provide a thermoplastic block component is a diaminehaving flexibility, which is a diamine including a flection structure,for example, an ether group, a sulfonic group, a ketone group, or asulfide group. The diamine preferably used is represented by thefollowing general Formula (1):

where R₄ is a group selected from a group including a bivalent organicgroup represented by General Formula Group (1):

where R₅ is one, identically or independently, selected from the groupconsisting of H—, CH₃—, —OH, —CF₃, —SO₄, —COOH, —CO—NH₂, Cl—, Br—, F—,and CH₃O—.

Preferable examples of diamine include 4,4′-diaminodiphenylpropane,4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl sulfide,3,3′-diaminodiphenylsulfone, 4,4′-diaminodiphenylsulfone,4,4′-oxydianiline, 3,3′-oxydianiline, 3,4′-oxydianiline,4,4′-diaminodiphenyldiethylsilane, 4,4′-diaminodiphenylsilane,4,4′-diaminodiphenylethylphosphine oxide, 4,4′-diaminodiphenylN-methylamine, 4,4′-diaminodiphenyl N-phenylamine,1,4-diaminobenzene(p-phenylenediamine),bis{4-(4-aminophenoxy)phenyl}sulfone,bis{4-(3-aminophenoxy)phenyl}sulfone, 4,4′-bis(4-aminophenoxy)biphenyl,4,4′-bis(3-aminophenoxy)biphenyl, 1,3-bis(3-aminophenoxy)benzene,1,3-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene,1,3-bis(3-aminophenoxy)benzene, 3,3′-diaminobenzophenone,4,4′-diaminobenzophenone, and 2,2-bis(4-aminophenoxyphenyl)propane.These may be used alone or in combination. The examples provided aboveare for the main component.

Any type of diamine may be used as the auxiliary component. Among thesecompounds, 4,4′-bis(4-aminophenoxy)biphenyl,4,4′-bis(3-aminophenoxy)biphenyl, 1,3-bis(3-aminophenoxy)benzene,1,3-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene,1,3-bis(3-aminophenoxy)benzene, and 2,2-bis(4-aminophenoxyphenyl)propaneare particularly preferable as the diamine.

Preferable examples of the acid component constituting the thermoplasticpolyimide precursor block component include, pyromellitic dianhydride,3,3′,4,4′-benzophenonetetracarboxylic dianhydride,3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 4,4′-oxydiphthalicdianhydride. These compounds may be used alone or in combination. In thepresent invention, it is preferable to use at least one acid dianhydrideselected from the group consisting of3,3′,4,4′-benzophenonetetracarboxylic dianhydride,3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 4,4′-oxydiphthalicdianhydride. By using these acid dianhydrides, high adherability to themetal layer, which is the advantage of the present invention, can beeasily achieved.

Preferable examples of the diamine and the acid dianhydride (diamine andacid dianhydride that are reacted with a prepolymer in the aboveprocesses 2) and 3)) used in producing the non-thermoplastic polyimideprecursor in combination with the thermoplastic polyimide precursorblock component are now described. Since properties change with thecombination of the diamine and the acid dianhydride, it is not feasibleto establish a general limitation. However, the main component of thediamine is preferably a rigid component, such as p-phenylene diamine orits derivative or benzidine or its derivative. The diamine having therigid structure can impart non-thermoplasticity and high elasticitymodulus.

The diamine component used to impart non-thermoplasticity to the endproduct polyimide resin is preferably a diamine having a rigidstructure. The diamine including the rigid structure in the presentinvention is represented by Formula (2):NH₂—R₂—NH₂  General Formula (2)where R₂ is a group selected from an bivalent aromatic group representedby General Formula Group (2):

where R₃ is one, identically or independently, selected from the groupconsisting of H—, CH₃—, —OH, —CF₃, —SO₄, —COOH, —CO—NH₂, Cl—, Br—, F—,and CH₃O—.

The acid component preferably contains pyromellitic dianhydride as themain component. As is well known in the art, pyromellitic dianhydrideeasily gives a non-thermoplastic polyimide due to its rigid structure.In this manner, the molecular design is determined so thatnon-thermoplasticity is imparted to the end product polyimide film.

Whether the resulting polyimide film is thermoplastic or not isdetermined by the following procedure. The polyimide film is fixed ontoa metal frame and heated at 450° C. for 1 minute. The film is assumed tobe non-thermoplastic when the heated film retains the original filmshape, i.e., when the heated film undergoes no relaxing or melting.

The linear expansion coefficient of the non-thermoplastic polyimide filmof the present invention is preferably 10 to 20 ppm. The moistureexpansion coefficient of the film is preferably 13 ppm or less. Theelasticity modulus of the film is preferably 5 to 10 GPa.

These physical properties usually change depending on the composition.In one aspect, it is possible to control the physical properties bychanging the choice of the thermoplastic block component of the presentinvention.

In the present invention, from the standpoint of simplicity of thepolymerization control and convenience of the facility, it is preferableto employ a polymerization process in which the non-thermoplasticpolyimide precursor is prepared by adding a diamine and/or an aciddianhydride in adequately designed molar fractions after the synthesisof the thermoplastic polyimide precursor block component.

Any solvent that dissolves the polyimide precursor (hereinafter alsoreferred to as “polyamic acid”) may be used in the synthesis of thepolyamic acid. Preferable examples include amide solvents such asN,N-dimethylformamide, N,N-dimethylacetamide, andN-methyl-2-pyrrolidone. N,N-Dimethylformamide and N,N-dimethylacetamideare particularly preferable.

A filler may be added to improve various properties of the film, such asslidability, thermal conductivity, electrical conductivity, coronaresistance, and loop stiffness. The filler may be any but preferablysilica, titanium oxide, alumina, silicon nitride, boron nitride, calciumhydrogen phosphate, calcium phosphate, or mica.

The diameter of the filler particles may be determined based on the filmproperties to be modified and the type of filler, and is thus notparticularly limited. The average particle diameter is usually 0.05 to100 μm, preferably 0.1 to 75 mm, more preferably 0.1 to 50 μm, and mostpreferably 0.1 to 25 μm. When the average diameter is below this range,the effect of modification is not readily exhibited. At an averagediameter beyond this range, the surface quality and/or the mechanicalproperties may be significantly degraded. The amount of the filler to beadded is determined based on the film properties to be modified and thediameter of the filler particles and is thus not particularly limited.The amount of the filler added is usually 0.01 to 100 parts by weight,preferably 0.01 to 90 parts by weight, and more preferably 0.02 to 80parts by weight per 100 parts by weight of polyimide. At a fillercontent below this range, the effect of the modification by the use ofthe filler may not be sufficiently exhibited. At a filler content abovethis range, the mechanical properties of the film may be significantlydegraded. The filler may be added by any method. The examples of themethod include:

1) Method of adding the filler to the polymerization solution before orduring the polymerization;

2) Method of adding and kneading the filler with a three-shaft rollerafter completion of the polymerization; and

3) Method of combining a polyamic acid organic solvent solution with adispersion containing the filler prepared in advance.

It is preferable to employ the method of combining the polyamic acidsolution with the filler-containing dispersion, in particular, a methodof combining the polyamic acid solution with the dispersion immediatelybefore the film forming since contamination of the manufacturing line bythe filler is least. In preparing the filler-containing dispersion, thesame solvent as the polymerization solvent for the polyamic acid ispreferably used. In order to sufficiently disperse the filler andstabilize the dispersion state, a dispersant, a thickener, or the likemay be used in amounts that do not adversely affect the properties ofthe film.

In a case where a filler is added to improve slidability of the film, aparticle diameter of the filler is in the range from 0.1 to 10 μm,preferably 0.1 to 5 μm. When the particle diameter is below this range,the effect of improvement in slidability is rarely obtainable. When theparticle diameter is above this range, it becomes difficult to form afine wiring pattern. Furthermore, in this case, a dispersion state ofthe filler is also important, and the number of a filler aggregate of 20μm or more per square meter is 50 or less, preferably 40 or less. Whenthe number of the filler aggregate of 20 μm or more is above this range,a generated fine wiring pattern has a smaller adhesion area, which tendsto decrease reliability of the FPC itself.

A known process may be employed to produce a polyimide film from thepolyamic acid solution. In particular, a thermal imidization process anda chemical imidization process are available. Either process may be usedto produce the film; however, the chemical imidization process tends toproduce a polyimide film having various properties preferred in thepresent invention.

The process for producing a polyimide film particularly preferred in thepresent invention preferably includes the steps of:

a) reacting an aromatic diamine and an aromatic tetracarboxylicdianhydride in an organic solvent to yield a polyamic acid solution;

b) flow-casting a film-forming dope containing the polyamic acidsolution onto a support;

c) heating the cast dope on the support and peeling off the resultinggel film from the support; and

d) further heating and drying the gel film to imidize the remaining amicacid.

In the steps described above, a curing agent including a dehydrator,e.g., an acid anhydride such as acetic anhydride; and an imidizationcatalyst, e.g., a tertiary amine such as isoquinoline, β-picoline, orpyridine, may be used.

A process for producing a polyimide film according to a preferredembodiment of the present invention, which is a chemical imidizationprocess, will now be described as an example. It should be understoodthat the invention is not limited by the examples below.

The film-forming conditions and heating conditions vary depending on thetype of polyamic acid, the thickness of the film, and the like.

A dehydrator and an imidization catalyst are mixed in a polyamic acidsolution at low temperature to prepare a film-forming dope. Thefilm-forming dope is then cast onto a support, such as a glass plate, analuminum foil, an endless stainless steel belt, or a stainless steeldrum, to prepare a film, and the film is heated at 80° C. to 200° C.,preferably at 100° C. to 180° C. to activate the dehydrator and theimidization catalyst. The resulting film thereby partly cured and/ordried is then separated from the support to obtain a polyamic acid film(hereinafter referred to as “gel film”).

The gel film is in the intermediate stage of curing the polyamic acid toa polyimide and has a self-supporting ability. The volatile componentcontent in the gel film determined by the following equation (3) is 50to 500 percent by weight:(A−B)×100/B  (3)wherein A is the weight of the gel film, and B is the weight of the gelfilm after 20 minutes of heating at 450° C. The volatile componentcontent is usually 5 to 500 percent by weight, preferably 5 to 200percent by weight, and more preferably 5 to 150 percent by weight. Afilm satisfying this range is preferably used; otherwise, problems suchas film breaking during the baking step, uneven color tone due to unevendrying, variations in characteristics, and the like may occur.

The amount of the dehydrator used is preferably 0.5 to 5 mol and morepreferably 1.0 to 4 mol per mole of the amic acid unit in the polyamicacid.

The amount of the imidization catalyst is 0.05 to 3 mol and preferably0.2 to 2 mol per mole of the amic acid unit in the polyamic acid.

When the content of the dehydrator and the imidization catalyst is belowthis range, chemical imidization proceeds insufficiently. Thus, breakingmay occur during the baking, or mechanical strength may be reduced. Whenthe content is beyond this range, the progress of imidization isexcessively accelerated, and it may be difficult to satisfactorily castthe solution into a form of film.

A polyimide film of the present invention is obtained by fixing the endsof the gel film to dry the film without shrinkage during the curing andto thereby remove water, the residual solvent, the residual convertingagent, and the catalyst. Then the residual amic acid is completelyimidized to give a polyimide film of the present invention.

Here, it is preferable to finally heat the film at a temperature in arange of 400° C. to 650° C. for 5 to 400 seconds. If the temperature isover this range and/or if the heating time is beyond this range, heatdeterioration of the film may occur. In contrast, if the temperature isbelow this range and/or if the heating time is below this range,expected effects may not be exhibited.

In order to reduce the internal stress remaining in the film, it ispossible to heat the film under the lowest possible tension required forfilm transfer. The heating process may be conducted in the film-formingprocess; alternatively, a separate heating process may be provided. Theheating conditions vary depending on the properties of the film or thedevice used. Although no general limitation can be introduced, thetemperature of the heating process is usually in the range of 200° C. to500° C., preferably 250° C. to 500° C., and most preferably 300° C. to450° C. and the heating time is usually 1 to 300 seconds, preferably 2to 250 seconds, and most preferably about 5 to 200 seconds, for reducingthe internal stress.

The polyimide film produced as such is a non-thermoplastic polyimidefilm that contains a non-thermoplastic polyimide resin having athermoplastic polyimide block component. The polyimide film produced assuch is also a non-thermoplastic polyimide film comprising:

a non-thermoplastic polyimide resin having at least one residue unitderived from a compound having diamine functionality and at least oneresidue unit derived from a compound having acid dianhydridefunctionality,

wherein either the residue unit derived from a compound having diaminefunctionality or the residue unit derived from a compound having aciddianhydride functionality has at least one amic acid group and exhibitsa thermoplastic character when bound linearly using pyromellitic aciddianhydride (in the case of the compound having diamine functionality)or p-phenylenediamine (in the case of the compound having aciddianhydride functionality) and then imidized.

The polyimide film produced as such is also a non-thermoplasticpolyimide film comprising:

a non-thermoplastic polyimide resin having at least one residue unitderived from a compound having diamine functionality and at least oneresidue unit derived from a compound having acid dianhydridefunctionality,

wherein either the residue unit derived from a compound having diaminefunctionality or the residue unit derived from a compound having aciddianhydride functionality has at least one imide group and exhibits athermoplastic character when bound linearly using pyromellitic aciddianhydride (in the case of the compound having diamine functionality)or p-phenylenediamine (in the case of the compound having aciddianhydride functionality) and then imidized.

This fact can be indirectly confirmed by comparing the physicalproperties according to the technique below. The technique forconfirming the presence of a thermoplastic polyimide-derived blockcomponent in the produced non-thermoplastic polyimide film is asfollows:

1) The monomer components of the non-thermoplastic polyimide film areanalyzed with liquid chromatography by decomposing polyimide with analkali such as hydrazine. When the film contains additives, such as afiller, the types and amounts of such additives are determined.2) The following random polymerization is conducted for a designatedcomposition:

i) The entire diamine is dissolved in DMF and the resulting solution iscooled in a 0° C. ice bath;

ii) To the resulting solution in the ice bath, powder of an aciddianhydride is gradually and carefully added under stirring so that nosedimentation occurs. A polyamic acid solution having a viscosity of2,500 to 4,000 poise (23° C.) is obtained as a result. When two or moreacid dianhydrides are used, the dianhydrides are mixed as powder andthen added.

3) A film is produced by the following process:

i) In a 500 cc polyethylene container, 100 g of the polyamic acidsolution is weighed and cooled to about 5° C. When a filler is to beused, the filler is preliminarily dispersed in the polyamic acidsolution.

ii) To the polyamic acid solution resulting from i), 50 g of animidization agent cooled to −10° C. and containing DMF and 0.8 mol ofisoquinoline and 2 mol of acetic anhydride per mole of amic acid isadded, and the resulting mixture is rapidly stirred.

iii) The solution resulting from ii) is degassed by centrifugation undercooling.

iv) The solution resulting from iii) is flow-cast onto an aluminum foilusing a comma coater.

v) The cast solution and the aluminum foil carrying the cast solutionare dried at 120° C. for 2 minutes, and the resulting gel film is peeledoff from the aluminum foil and fixed onto a metal fixing frame. Here,caution must be paid not to shrink the gel film.

vi) The gel film fixed on the metal fixing frame is heated at 300° C.for 1 minute, at 400° C. for 1 minute, and at 450° C. for 1 minute in apreliminarily heated hot-air circulation oven, and is separated from thefixing frame to obtain a polyimide film having a thickness of 25 μm.

4) The comparison of the physical properties between the film thusobtained (hereinafter also referred to as the “comparative film”) andthe film prepared by the polymerization according to the presentinvention in which the thermoplastic polyimide block component isincorporated (hereinafter also referred to as the “inventive film”)finds the following features:

i) The inventive film has an elasticity modulus higher than that of thecomparative film by at least 0.3 GPa and in particular by at least 1GPa.

ii) The inventive film has a linear expansion coefficient and moistureexpansion coefficient smaller than those of the comparative film by atleast 1 ppm and in particular by at least 3 ppm.

iii) Both films maintain substantially the same tensile elongation.

iv) The storage elasticity modulus of the inventive film at 380° C.determined by dynamic viscoelasticity analysis is lower than that of thecomparative film by at least 0.1 GPa and in particular by at least 0.3GPa.

The tan δ peak value of the inventive film is larger than that of thecomparative film by at least 0.01 and in particular by at least 0.02.

The following will describe the metal layer according to the presentinvention. The metal layer preferably includes a metal layer A producedby dry film formation. The metal layer A is formed on at least onesurface of the polyimide film, and functions to tightly adhere to anelectroless plated layer if the electroless plated layer is formed inthe following process. Dry film formation (dry plating) is preferablyadopted for producing the metal layer A because there is no need forapplying plating catalyst onto the polyimide film to produce the metallayer A, and no plating catalyst therefore remains on the polyimidefilm.

Examples of a method for forming the metal layer A by dry platinginclude vacuum vapor deposition, sputtering, ion plating, and CVD(chemical vapor deposition).

Among the methods taken above, physical vapor deposition is preferableto form a metal layer since the physical vapor deposition exhibitsexcellent adherability. The physical vapor deposition includes vacuumvapor deposition and sputtering. Examples of the vacuum vapor depositioninclude resistance heating vapor deposition, EB deposition, cluster ionbeam deposition, and ion plating deposition. Examples of the sputteringinclude RF sputtering, DC sputtering, magnetron sputtering, and ion beamsputtering. Any one or combination of these methods can be applied tothe present invention.

Further, among these methods, sputtering methods are preferable from thestandpoint of adhesive strength between the polyimide film and the metallayer A, simplicity of the facility, productivity, and cost. Among thesputtering methods, DC sputtering is particularly preferable. Also, ionplating deposition is industrially useful since it exhibits rapid filmformation, and preferably employed since it exhibits excellentadherability.

Especially, the case where sputtering is adopted will be described indetail. A known method can be adopted as sputtering. That is, DCmagnetron sputtering, RF sputtering, or these sputtering methods withvarious improvements can be adopted appropriate to the needs. Forexample, DC magnetron sputtering is preferable for an efficientsputtering of a conductor such as nickel and copper, whereas RFsputtering is preferable for sputtering under high vacuum for thepurpose of preventing contamination of sputter gas in a thin film or thelike purpose.

More specifically, DC magnetron sputtering is carried out as follows:First, the polyimide film is set in a vacuum chamber for vacuum suction(vacuuming). Generally, vacuum suction is performed by using a rotarypump for rough vacuuming in combination with a diffusion pump, acryopump, or a turbo pump until the pressure inside the vacuum chamberreaches 6×10⁻⁴ Pa or lower. Then, sputter gas is introduced into thechamber until the pressure inside the chamber reaches 0.1 to 10 Pa,preferably 0.1 to 1 Pa, and DC voltage is applied to a target metal sothat plasma discharge occurs. In this case, the efficiency of sputteringfor the deposition of plasma particles onto the target is enhanced byconfining generated plasma in a magnetic field formed on the target.Under the situation where plasma is generated for several minutes toseveral hours, a surface oxidation layer is removed from the targetmetal (This process is called “pre-sputtering”). In this case, cautionmust be paid so that adverse effects caused by plasma or sputtering arenot exerted on the polymer film. After the pre-sputtering is completed,the polyimide film is subjected to sputtering with a shutter opened orby the other operation. Discharge power at the sputtering is preferablyin the range from 100 to 1000 watts. Batch sputtering or roll sputteringis adopted depending on the shape of a sample to be subjected tosputtering. The sputter gas to be introduced is generally inactive gassuch as argon; however, a mixed gas containing small amount of oxygen orother gas can be employed.

The metal layer A is preferably made from a metal which has a highadhesive strength to the polyimide film and a circuit pattern formed onthe metal layer A in the following circuit board producing process andallows clean removal in the etching process included in the method forproducing a printed wiring board of the present invention. For example,the metal layer A can be made from metal such as Ni, Cu, Mo, Ta, Ti, V,Cr, Fe, Co, or alloy of any of these metals. Further, the metal layer Acan be made up of a single layer or two or more layers made from any ofthese metals.

In an embodiment of the metal layer A of the present invention, amaterial for the metal layer A is preferably copper. Also, copper and atleast one metal selected from the group consisting of Ni, Cu, Mo, Ta,Ti, V, Cr, Fe, Co can be employed as the material for the metal layer A.That is, the metal layer A may be (i) made from copper, (ii) made fromalloy (complex) of copper and at least one metal selected from the abovegroup, or (iii) made up of two layers in which one layer is made from atleast one metal selected from the above group and the other layer ismade from copper.

A thickness of the metal layer A, which may be determined asappropriate, is 1000 nm or less, preferably in the range from 2 to 1000nm, more preferably in the range from 2 to 500 nm. A metal layer Ahaving a thickness of less than 2 nm tends to exert an unstable peelstrength.

In another embodiment of the metal layer A of the present invention, themetal layer A is of a two-layer structure having two types of metallayers, and thicknesses of the two layers are adjusted to appropriatethicknesses. A metal layer directly formed on the polyimide film isreferred to as a metal layer A1, and a metal layer formed on the metallayer A1 is referred to as a metal layer A2. The structure with twotypes of metal layers allows for the improvement in etching properties,adherability to a polymer film, peel strength to an electroless platedfilm and an electroplated film, and the like property. That is, as themetal layer A1 directly formed on the polymer film, a metal that iseffective to maintain excellent adherability to the polyimide film isselected. On the other hand, as the metal layer A2 formed on the metallayer A1, it is effective to select a metal that can be tightly adheredto an electroplated layer directly formed on the metal layer A2 or anelectroless plated layer formed in a panel plating process.

A metal used for the metal layer A1 is preferably Ni, Cu, Mo, Ta, Ti, V,Cr, Fe, Co, and the like, and nickel is especially preferable. Athickness of the metal layer A1 is preferably in the range from 2 to 200nm, more preferably in the range from 3 to 100 nm, especially preferablyin the range from 3 to 30 nm. A thickness of less than 2 nm is notpreferable since it cannot exert sufficient bonding strength, and makesit difficult to uniformly form the metal layer A1 on the polymer. On theother hand, a thickness of more than 200 nm requires extra etching inthe etching process during the production of a printed wiring board, andmay therefore result in a circuit thinner than designed, a circuit witha smaller width, the occurrence of undercut or the like phenomenon, acircuit in degraded form. In addition, peeling of the film, curling ofthe film, or the like problem occurs due to difference in dimensionalchange between the metal layer A1 and the metal layer A2.

Meanwhile, a metal used for the metal layer A2 may be determinedaccording to the type of plating directly formed on the metal layer A2in the process of producing a printed wiring board, i.e. whether anelectro plating or an electroless plating. Considering that theelectroless plating is preferably an electroless copper plating and anelectroless nickel plating, especially preferably an electroless copperplating as will be described later, a metal used for the metal layer A2is preferably copper and nickel, especially preferably copper. Athickness of the metal layer A2 is suitably in the range from 10 to 300nm, more suitably in the range from 20 to 200 nm, preferably in therange from 50 to 150 nm. A thickness of less than 10 nm makes itdifficult to maintain sufficient adherability to an electroless platedlayer formed in the following process. On the other hand, a thickness ofmore than 200 nm is not needed. A thickness of the metal layer A2 isdesirably 200 nm or less in consideration of the following etchingprocess.

A thickness of the metal layer A obtained when the metal layer A1 iscombined with the metal layer A2 is preferably in the range from 20 to400 nm, more preferably 50 to 200 nm.

It is preferable that dry plating is continuously performed in vacuum.In this case, dry plating is preferably vapor deposition and sputtering,more preferably sputtering, especially preferably DC sputtering.

In a case where dry plating is adopted in the process in which the metallayer is directly formed on the polyimide film without using anadhesive, vacuum suction is performed in the course of dry plating.Therefore, it is desirable that a state within the system is changed toa nearly vacuum state as soon as possible in consideration ofproductivity.

As noted above, the non-thermoplastic polyimide film used in themetal-coated polyimide film of the present invention has a high watervapor transmission rate. It has surprisingly been found that polyimidefilms having the indicated high water vapor transmission rate arerapidly conditioned under vacuum to be ready for formation of a metallayer directly and without use of an adhesive. As a result of this, themethod using a non-thermoplastic polyimide film is advantageous in thatit allows the production of the metal-coated polyimide product at ahigher speed and in very high quality when the metal layer is formedthereon by dry plating such as sputtering.

The non-thermoplastic polyimide film used in the present invention ispreferably used in directly forming a metal layer thereon due to itshigh water vapor transmission rate and its quick conditioning in thevacuum chamber.

The water vapor transmission rate varies depending on the thickness ofthe film. For this reason, a value represented by following equation (3)is used as a property of the water vapor transmission.Water Vapor Transmission Rate Value=water vapor transmissionrate×thickness  (3)

No commercially available film having the value represented from theequation (3) of at least about 2500 μm·g/m²/24 h has been found.Preferably, the Water Vapor Transmission Rate Value is at least about3000 μm·g/m²/24 h.

This value was derived from the fact that the water vapor transmissionrate is inversely proportional to the thickness of the film as shown inthe graph of FIG. 1. In the graph of FIG. 1, the inclination of eachline (3503.2, 1723.1, 594.58, and 153.5; horizontal axis: 1/(thickness))indicates a value of “water vapor transmission rate×thickness.”

INDUSTRIAL APPLICABILITY

The metal-coated polyimide film of the present invention exhibitsexcellent adherability although it has a metal layer directly formedthereon without using an adhesive. The metal-coated polyimide film ofthe present invention can be therefore suitably used for a flexibleprinted wiring board, TAB tape, and other materials.

EXAMPLES

The present invention will now be described in specifics by way ofexamples. It is to be understood that the present invention is notlimited to these examples.

(Dynamic Viscoelasticity Measurement)

Storage modulus was measured with DMS-600 produced by Seiko InstrumentsInc. under the following conditions. As a result of the measurement,storage modulus at 380° C. and tan δ peak value were obtained.

Temperature profile: 0 to 400° C. (3° C./min)

Sample size: 9 mm in width, distance between holding tools: 20 mm

Frequency: 5 Hz

Strain amplitude: 10 μm

Minimum tension: 100

Tension gain: 1.5

Initial value of force amplitude: 100 mN

(Initial Metal Foil Peel-Strength)

In accordance with Japanese Industrial Standard C-6471, a 1-mm metalpattern was evaluated in 90-degree peel strength test.

(Metal Foil Peel-Strength: Bonding strength after PCT (Pressure CookerTest))

A sample prepared as in the measurement of the initial bonding strengthwas introduced into a pressure cooker tester PC-422RIII (Product name)produced by Hirayama Manufacturing Corporation, and left for 96 hours at121° C. and 100% R.H. Then, bonding strength of the sample taken out ofthe tester was measured as in the measurement of the initial bondingstrength.

(Identification of Thermoplasticity)

A polyimide film containing a thermoplastic polyimide block componentwas prepared at a maximum baking temperature of 300° C. for a bakingtime of 15 minutes. The film was fixed on a metal fixing frame andheated at 450° C. for 1 minute. The film was assumed to be thermoplasticwhen the film softened and did not retain its original shape.

(Moisture Expansion Coefficient)

The length (L1) of a film was measured at 50° C. and 30% R.H., thehumidity was then increased to 80% R.H., and the length (L2) of the filmat 50° C. and 80% R.H. was measured. The moisture expansion coefficientwas determined by the following equation:Moisture Expansion Coefficient (ppm)=(L2−L1)/L1/(80−30)×10⁶

(Linear Expansion Coefficient)

The linear expansion coefficient of the polyimide film obtained wasmeasured by using Thermo-mechanical Analysis Instrument TMA/SS6100manufactured by SIT Nanotechnology Inc. To measure the linear expansioncoefficient, the polyimide film was heated from 0 to 460° C., and thencooled down to 10° C. After that, the polyimide film was heated at theheating rate of 10° C./min. The polyimide film was measured at 100° C.and 200° C. in the second heating. The measurement values were averagedto work out the linear expansion coefficient of the polyimide film.

Sample size: 3 mm in width, 10 mm in length

Load: 29.4 mN

Temperature range in measurement: 0 to 460° C.

Heating rate: 10° C./min

(Elasticity Modulus and Elongation)

The elasticity modulus was measured according to the standard D882 ofAmerican Society of Testing and Materials (ASTM).

(Measurement of Water Vapor Transmission Rate)

In accordance with the Japanese Industrial Standard Z0208, measurementwas conducted at a temperature of 40° C. and at 90% relative humidity.

Example 1

In 546 g of N,N-dimethylformamide (DMF) cooled to 10° C., 46.43 g of2,2-bis(4-aminophenoxyphenyl)propane (BAPP) was dissolved. To thissolution, 9.12 g of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride(BTDA) was added and dissolved. Then, 16.06 g of pyromelliticdianhydride (PMDA) was added and the resulting mixture was stirred for30 minutes to obtain a thermoplastic polyimide precursor blockcomponent.

In this solution, 18.37 g of p-phenylenediamine (p-PDA) was dissolved,and then 37.67 g of PMDA was added to the resulting solution anddissolved by stirring for 1 hour. A separately prepared DMF solution ofPMDA (PMDA 1.85 g/DMF 24.6 g) was carefully added to the resultingsolution, and the addition was ceased when the viscosity reached about3,000 poise. Stirring was continued for 1 hour to obtain a polyamic acidsolution having a solid content of about 19 wt % and a rotationalviscosity at 23° C. of 3,400 poise.

To 100 g of this polyamic acid solution, 50 g of a curing agent composedof acetic anhydride/isoquinoline/DMF (ratio of 18.90/7.17/18.93 based onweight) was added, and the resulting mixture was stirred and degassed ata temperature of 0° C. or lower. The mixture was then flow-cast on analuminum foil using a comma coater.

This resin film was heated at 130° C. for 150 seconds. The resultingself-supporting gel film (residual volatile component content: 45 wt %)was peeled from the aluminum foil, fixed on a metal frame, and dried at300° C. for 20 seconds, 450° C. for 20 seconds, and 500° C. for 20seconds for imidization to obtain a polyimide film having a thickness of38 μm. The obtained polyimide film was fixed on a metal fixing frame,and heating the fixed film at 450° C. was attempted. However, the filmdid not change its appearance. It was confirmed that the film wasnon-thermoplastic.

The surface of the polyimide film was subjected to ion gun processing at200 V, 10 mA for 60 seconds. Thereafter, by using a sputtering apparatus(produced by Showa Shinku Co., Ltd), 50 angstrom of nickel was laminatedon the surface of the polyimide film. Further, 2000 angstrom of copperwas laminated on the nickel lamination layer. Still further, the copperlamination layer was treated by sulfate electric copper plating (cathodecurrent density: 2 A/dm2, plating thickness: 20 μm, 20 to 25° C.) was toprepare a metal-coated polyimide film.

The properties of the obtained metal-coated polyimide film are shown inTable 1. In Table 1, polymerization recipe is shown in molar ratio.

A film was prepared by using a polyamic acid solution withBAPP/BTDA/PMDA=46.43 g/9.12 g/18.53 g. As a result of thethermoplasticity determination of the thermoplastic block component, itwas confirmed that the thermoplastic block component hasthermoplasticity.

Examples 2 Through 4

A metal-coated polyimide film was prepared as in EXAMPLE 1 but with adifferent monomer ratio. The properties of the films obtained are shownin Tables 1 and 2.

In EXAMPLES 2 and 3, the confirmation of the thermoplastic blockcomponent was conducted as in EXAMPLE 1, and it was confirmed that thethermoplastic block component has thermoplasticity.

Comparative Example 1 Film with No Thermoplastic Block Component

In 546 g of N,N-dimethylformamide (DMF) cooled to 10° C., 18.37 g ofp-phenylenediamine (p-PDA) was dissolved. To this solution, 33.56 g ofpyromellitic dianhydride (PMDA) was added and the resulting mixture wasstirred for 30 minutes to obtain a block component.

In this solution, 46.43 g of 2,2-bis(4-aminophenoxyphenyl)propane (BAPP)was dissolved, and then 9.12 g of 3,3′,4,4′-benzophenonetetracarboxylicdianhydride (BTDA) was added to the resulting solution. Thereafter,22.24 g of PMDA was added to the solution and dissolved by stirring for1 hour. A separately prepared DMF solution of PMDA (PMDA 1.85 g/DMF 24.6g) was carefully added to the resulting solution, and the addition wasceased when the viscosity reached about 3,000 poise. Stirring wascontinued for 1 hour to obtain a polyamic acid solution having a solidcontent of about 19 wt % and a rotational viscosity at 23° C. of 3,400poise. By using the obtained polyimide acid solution, a metal-coatedpolyimide film was obtained as in EXAMPLE 1. The properties of themetal-coated polyimide film are shown in Table 2. Plasticitydetermination of the block component was conducted as in EXAMPLE 1, andit was confirmed that the block component was non-thermoplastic.

Comparative Example 2 Film with No Thermoplastic Block Component

In 546 g of N,N-dimethylformamide (DMF) cooled to 10° C., 18.37 g ofp-phenylenediamine (p-PDA) and 46.43 g of2,2-bis(4-aminophenoxyphenyl)propane (BAPP) were dissolved. To thissolution, 9.12 g of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride(BTDA) and 53.73 g of pyromellitic dianhydride (PMDA) were added and theresulting mixture was dissolved by stirring for 1 hour. A separatelyprepared DMF solution of PMDA (PMDA 1.85 g/DMF 24.6 g) was carefullyadded to the resulting solution, and the addition was ceased when theviscosity reached about 3,000 poise. Stirring was continued for 1 hourto obtain a polyamic acid solution having a solid content of about 19 wt% and a rotational viscosity at 23° C. of 3,000 poise. By using theobtained polyimide acid solution, a metal-coated polyimide film wasobtained as in EXAMPLE 1. The properties of the metal-coated polyimidefilm are shown in Table 2.

Comparative Example 3

As a result of the measurement of water vapor transmission rate of 38 mmof Apical HP (produced by Kaneka Corporation) was measured, and it was 5g/m²/24 h.

Reference Example 1 Film with No Thermoplastic Block Component

In 546 g of N,N-dimethylformamide (DMF) cooled to 10° C., 46.43 g of2,2-bis(4-aminophenoxyphenyl)propane (BAPP) and 18.37 g ofp-phenylenediamine (p-PDA) were dissolved. To this solution, 9.12 g of3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and 53.73 g ofpyromellitic dianhydride (PMDA) were added and dissolved by stirring for1 hour. A separately prepared DMF solution of PMDA (PMDA 1.85 g/DMF 24.6g) was carefully added to the resulting solution, and the addition wasceased when the viscosity reached about 3,000 poise. Stirring wascontinued for 1 hour to obtain a polyamic acid solution having a solidcontent of about 19 wt % and a rotational viscosity at 23° C. of 3,400poise.

To 100 g of this polyamic acid solution, 50 g of a curing agent composedof acetic anhydride/isoquinoline/DMF (ratio of 16.96/8.58/24.46 based onweight) was added, and the resulting mixture was stirred and degassed ata temperature of 0° C. or lower. The mixture was then flow-cast on analuminum foil using a comma coater. This resin film was heated at 120°C. for 2 minutes. The resulting gel film was peeled from the aluminumfoil and fixed on a metal frame with care to prevent shrinkage of thegel film. The gel film fixed on the metal frame was heated at 300° C.for 1 minute, 400° C. for 1 minute, and 450° C. for 1 minute in apreheated circulating hot air oven. Then, the gel film was removed fromthe frame to obtain a polyimide film having a thickness of 38 μm. Byusing the obtained polyimide film, a metal-coated polyimide film wasobtained as in EXAMPLE 1. The properties of the metal-coated polyimidefilm are shown in Table 2.

TABLE 1 EXAMPLE 1 EXAMPLE 2 EXAMPLE 3 EXAMPLE 4 POLYMERIZATION RECIPEBAPP 40 BAPP 50 BAPP 40 ODA 20 BTDA 10 BTDA 40 BTDA 10 BAPP 30 PMDA 26PDA 50 PMDA 22 BTDA 20 PDA 60 PMDA 60 PDA 60 PMDA 25 PMDA 64 PMDA 68 PDA50 PMDA 55 NO. OF REPEATING UNITS OF BLOCK COMPONENT 9 4 4 9 CONTENT OFTHERMOPLASTIC BLOCK COMPONENT 40 50 40 50 WATER VAPOR TRANSMISSION RATE170 g/m²/24 h 190 g/m²/24 h 160 g/m²/24 h 130 g/m²/24 h ELASTICITYMODULUS (GPa) 7.3 6.1 6.5 6.8 ELONGATION (%) 45 60 48 55 LINEAREXPANSION COEFFICIENT 11 22 14 11 MOISTURE EXPANSION COEFFICIENT 9 11 1010 TAN δ PEAK VALUE 0.10 0.13 0.08 0.15 STORAGE MODULUS AT 380° C. 1.10.9 1.2 0.8 BONDING STRENGTH (N/cm) INITIAL VALUE 8.5 7.3 8.6 8.0 VALUEAFTER PCT 4.3 4.0 4.6 4.5

In Example 1, the thermoplastic block component was composed of threecomponents in the polymerization recipe, BAPP/BTDA/PMDA (monomerratio=40/10/26) in Table 1.

In Example 2, the thermoplastic block component was composed of the twocomponents in the polymerization recipe, BAPP/BTDA (monomer ratio=50/40)in Table 1.

In Example 3, the thermoplastic block component was composed of thethree components in the polymerization recipe, BAPP/BTDA/PMDA (monomerratio=40/10/22) in Table 1.

In Example 4, the thermoplastic block component was composed of the fourcomponents in the polymerization recipe, ODA/BAPP/BTDA/PMDA (monomerratio=20/30/20/25) in Table 1.

TABLE 2 COMPARATIVE COMPARATIVE REFERENCE EXAMPLE 1 EXAMPLE 2 EXAMPLE 1POLYMERIZATION RECIPE PDA 60 PDA 60 BAPP 40 PMDA 54 BAPP 40 PDA 60 BAPP40 BTDA 10 BTDA 10 BTDA 10 PMDA 90 PMDA 90 PMDA 36 NO. OF REPEATINGUNITS OF BLOCK COMPONENT — — — CONTENT OF THERMOPLASTIC BLOCK COMPONENT— — — WATER VAPOR TRANSMISSION RATE 100 g/m²/24 h 100 g/m²/24 h 110g/m²/24 h ELASTICITY MODULUS (GPa) 7.1 6.2 6.0 ELONGATION (%) 15 45 50LINEAR EXPANSION COEFFICIENT 10 17 15 MOISTURE EXPANSION COEFFICIENT 914 13 TAN δ PEAK VALUE 0.10 0.07 0.07 STORAGE MODULUS AT 380° C. 1.1 1.41.8 BONDING STRENGTH (N/cm) INITIAL VALUE 4.0 4.2 5.1 VALUE AFTER PCT2.5 2.0 1.5

Example 5

A polyimide film having a thickness of 10 μm was prepared as in EXAMPLE4 except that the resin film on the aluminum foil was heated at 110° C.for 70 sec and the self-supporting gel film fixed on a metal frame wasdried at 300° C. for 20 seconds, and 450° C. for 40 seconds forimidization as shown in Table 3. The Water Vapor Transmission Rate ofthe film obtained is shown in Table 3. A comparison with thecommercially available films, A (Apical NPI (produced by KanekaCorporation), B (Apical HP (produced by Kaneka Corporation), C is shownin the graph of FIG. 1.

Example 6

A polyimide film having a thickness of 12.5 μm was prepared as inEXAMPLE 4 except that the resin film on the aluminum foil was heated at120° C. for 70 sec and the self-supporting gel film fixed on a metalframe was dried at 300° C. for 20 seconds, and 450° C. for 40 secondsfor imidization as shown in Table 3. The Water Vapor Transmission Rateof the film obtained is shown in Table 3. A comparison with thecommercially available films, A (Apical NPI (produced by KanekaCorporation), B (Apical HP (produced by Kaneka Corporation), C is shownin the graph of FIG. 1.

Example 7

A polyimide film having a thickness of 17 μm was prepared as in EXAMPLE4 except that the resin film on the aluminum foil was heated at 135° C.for 70 sec and the self-supporting gel film fixed on a metal frame wasdried at 300° C. for 20 seconds, 450° C. for 20 seconds, and 460° C. for20 seconds for imidization as shown in table 3. The Water VaporTransmission Rate of the film obtained is shown in Table 3. A comparisonwith the commercially available films, A (Apical NPI (produced by KanekaCorporation), B (Apical HP (produced by Kaneka Corporation), C is shownin the graph of FIG. 1.

Example 8

A polyimide film having a thickness of 25 μm was prepared as in EXAMPLE4 except that the resin film on the aluminum foil was heated at 130° C.for 130 sec and the self-supporting gel film fixed on a metal frame wasdried at 300° C. for 20 seconds, 450° C. for 20 seconds, and 480° C. for20 seconds for imidization as shown in Table 3. The Water VaporTransmission Rate of the film obtained is shown in Table 3. A comparisonwith the commercially available films, A (Apical NPI (produced by KanekaCorporation), B (Apical HP (produced by Kaneka Corporation), C is shownin the graph of FIG. 1.

TABLE 3 Example 5 Example 6 Example 7 Example 8 thickness of 10 12.5 1725 the film (μm) The Water 340 270 210 150 Vapor Transmission Rate ofthe film (g/m2/24 h)

1. A method of preparing a metal-coated polyimide film comprising: a)providing a non-thermoplastic polyimide film in a thickness of from 10to 75 microns having the value represented by following equation (3):a water vapor transmission rate×thickness  (3) of at least 2500μm·g/m²/24 h; b) applying vacuum suction to the polyimide film; and c)forming a metal layer directly on the polyimide film by a dry filmforming method without using an adhesive, wherein the non-thermoplasticpolyimide film, when fixed onto a metal frame and heated from 450° C.for one minute, retains its original film shape.
 2. The method of claim1, wherein the non-thermoplastic polyimide film has a value representedby following equation (3) of at least about 3000 μm·g/m²/24 h.
 3. Themethod of claim 1, wherein the dry film forming method is a methodselected from sputtering, ion plating, and vapor deposition.
 4. Themethod of claim 1, wherein the thermoplastic polyimide film is providedin a thickness of from 10 to 38 microns.